Included file not found error leaks full path to source directory

[benbalter]

Seems that since #1841 (and released with 1.4.3), requests for included files that do not exist within the _includes directory leak the absolute path to the source, not the relative path to the requesting file as they did before (and all other errors do).

Steps to reproduce

1. Create an `index.html file
2. Add {% include missing.html %} to it (don't create the missing file, duh)
3. jekyll build

Expected output:

Liquid Exception: Included file 'missing-file.html' not found in index.html

Actual output

Liquid Exception: Included file '/Users/benbalter/.../missing-file.html' not found in index.html

/cc @jens-na

[parkr]

Need this now or can we punt until 2.0.0?

[benbalter]

Minor, although theoretically a security concern if not properly sanitized elsewhere. May be a liquid thing all together.

[mattr-]

(don't create the missing file, duh)

❤️